Hydrocarbon recovery wells conventionally involve sequential casing strings, with each string being smaller in diameter than the next outer string. Each casing string may be secured with a casing hanger to a casing hanger housing. The annulus between differing diameter casing strings is conventionally filled with cement to a level that overlaps the bottom of the larger diameter casing string. The cement bonds with the open soil and with larger diameter casing strings to form an annular seal in a lower portion of the well. The casing string typically has a mechanical seal on the casing hanger that forms an upper barrier for the annulus between the casing strings. The seal on top of the annulus on the casing hanger and the seal on the bottom provided by the cement form a closed, fluid filled annulus.
If the well is brought into production, the production tubing will provide the flow path with oil or gas to the surface production equipment. During production, the tubing experiences temperature changes due to reservoir fluid temperature, which may be substantial. The heat from the production tubing is liberated to the surrounding larger casing strings and annuli. If the temperature of the fluid in the annuli rises, so does fluid pressure. If the increased pressure is not allowed to vent, it may burst the larger casing or collapse the smaller casing. Collapsed casing will likely damage control lines controlling the flow of the hydrocarbons through the production tubing, and may create environmental and safety concerns by not being able to close downhole valves along the production tubing string.
A rupture disk or blowout plug in a well will allow trapped pressure to vent to an area that is not trapped, and may eventually vent to the atmosphere, which may be hydrostatic sea pressure. Rupture disks may be placed into the tubular connectors which couple the casing joints together to form the casing string, as disclosed in U.S. Pat. No. 6,457,582. Rupture disks and blowout plugs have also been placed in a casing hanger to control the pressure differential between the interior of the casing string hung by the casing hanger and the outer casing, wellhead or other support housing surrounding and supporting the casing hanger. In this application, the rupture disk may be selectively ruptured to monitor annulus pressure at the surface, but does not prevent collapse of the casing.
The disadvantages of the prior art are overcome by the present invention. Improved fluid pressure control in a well is provided by the present invention.